1. Field of the Invention
The present invention relates to a safety switch which is mounted on the wall surface of a doorway of a room in which, for example, industrial machinery is installed, and which is capable of interrupting the power supply to the industrial machinery, etc. when the door of the doorway is opened.
2. Description of the Related Art
In industrial plants containing heavy machinery, there are hazardous driving zones established because of the likelihood of injuries to workers. Consequently, in order to prevent these dangers, a so-called lock system has been required to be installed, in which driving of the machine is stopped when the door of the doorway in the room or a danger zone is not completely closed.
For such a lock system, conventionally, a system to install limit switches at the sliding portions of the door and to supply power to the industrial machinery installed in the room only when the door closed condition is detected by the limit switches has been adopted.
However, because with this kind of lock system, operation of the machine inside the room is enabled by operating an actuator (section) of the limit switch, there is a defect for a safety countermeasure. To solve this kind of defect, there is proposed a safety switch which has a construction for preventing this kind of erroneous operation (Japanese Non-examined Patent Publication No. Hei 6-76674).
The safety switch of this proposal is a switch which has a construction in which special-purpose actuator fixed to the door enters the operating portion of the switch proper mounted to the wall surface in the circumference of the doorway of the room when the door of the doorway is closed, and with this action, the mobile contact (mobile piece) of the contact block is changed over, and this kind of change-over operation, the circuit connection is changed over to the main circuit side (power supply circuit to industrial machinery), causing the machines inside the room to be ready for operation. Now, there is no special problem in functions, safety, etc. with the safety switch disclosed in Japanese Non-examined Patent No. Hei 6-76674, but recently, as applications of safety switch of this kind are diversified, demands of a small-size safety switch which requires small installation space have increased.